In spite of the broad success of Total Knee Arthroplasty (TKA), problems of clinical function and implant durability persist, especially with regard to the patello-femoral joint. The premise for the proposed study is that in order to make significant further improvement in clinical success rates of TKA it is necessary to develop better understanding of the influence of geometric factors on joint mechanics. The specific aims focus on the influence of patella/joint line geometric parameters on extensor mechanism and joint contact forces. They include: 1) measuring radiographically in a series of normal knees geometric parameters to provide a base-line for evaluating effects of patella vs. joint line positioning following TKA; 2) measuring in a series of intact patellar ligament and quadriceps tendon forces during flexion-extension cycling for a series of superior-inferior patellar ligament insertion positions; 3) measuring in a series of knees with instrumented TKA'S, patellar ligament forces and quadriceps tendon forces during flexion-extension cycling for a series of patellar ligament insertion positions. In the radiographic study, geometric measures will be obtained from x-rays from routine diagnostic examinations to develop the statistical data base defining normal knee geometry. Fresh-frozen knees will be tested in a "quadriceps-driven" test apparatus which can produce continuous flexion-extension cycling. Superior-inferior patellar ligament insertion position will be altered using an adjustable positioning fixture mounted in the tibia. Patellar-femoral and tibial-femoral contact forces will be obtained using six-degree-of-freedom tibial component and patellar component load cells. The data obtained will be used to define how superior-inferior alterations of patellar ligament insertion position affect extensor mechanism forces and joint contact forces, and how they relate to preoperative geometry and mechanics.